Mold oscillator

ABSTRACT

A mold oscillator includes a ball screw unit that has a ball screw  32  having a threaded shaft  29  and a ball nut  30,  and has a nut-side shaft  31  fixed to the ball nut  30  coaxially with the threaded shaft  29,  wherein the ball screw unit is positioned so that the central axis of the ball screw unit extends in the vertical direction. A casing surrounds at least part of the ball screw  32.  The ball nut  30  of the ball screw  32  and part of the threaded shaft  29  of the ball screw  32,  on which, part the ball nut  30  is engaged with the threaded shaft  29,  are submerged in a lubricating oil so as to be able to lubricate the ball screw  32  with an oil bath.

TECHNICAL FIELD

The present invention relates to a mold oscillator for oscillating amold to reduce friction between the mold and a surface of a cast piecein a continuous casting machine for continuously casting steel or thelike.

BACKGROUND ART

In a continuous casting machine for continuously casting steel, moltensteel is poured from a tundish into a rectangular tube-shaped mold andthe molten steel is cooled through contact with the mold, a cast piece,in which unsolidified steel is present at the center portion thereof, iscontinuously drawn downward, and molten steel is continuously pouredinto the mold. The cast piece drawn downward out of the mold is watercooled by water spray. Finally, after completely solidified, the castpiece is cut into pieces of predetermined length and sent to adownstream process, that is, rolling.

In the mold, molten steel is brought into contact with the inner sidesurface of the mold, so that the molten steel is cooled and a solidifiedshell is formed. In order to prevent the solidified shell from adheringto the inner side surface of the mold, the mold is oscillated in thevertical direction (Patent Document 1). This prevents the cast piecefrom adhering to the inner side surface of the mold, so that it ispossible to smoothly draw the cast piece out of the bottom of the mold.

FIG. 8 is a schematic diagram showing an eccentric cam-type moldoscillator. As shown in FIG. 8, an arm support, portion 3 is mounted ona partition wall 6. One end port ton of a sub-arm 4 and a midpointportion of a main arm 5 are respectively supported in a swingable mannerby horizontal pivot shafts 3 a and 3 b provided in the arm supportportion 3. A mold 1 is supported on an oscillation table 2 andoscillated together with the oscillation table 2. The other end portionof the sub-arm 4 and one end pardon of the main arm 5 are respectivelyconnected to horizontal pivot shafts a and 2 b of the oscillation table2 in a swingable manner. In this way, the main arm 5 and the sub-arm 4constitute a parallel link, so that the four points, the pivot shafts 3a, 3 b, 2 b and 2 a, operate in relation to one another with distancestherebetween being fixed. The distance between the pivot shafts 2 a and2 b, the distance between the pivot shafts 3 a and 3 b, the distancebetween the pivot shafts 3 a and 2 a, and the distance between the pivotshafts 3 b and 2 b are set so that extensions of line segments 2 c and 2d cross each other at a swing arm center 1 a, the line segment 2 cconnecting between the pivot shaft 3 a and the pivot shaft 2 a, the linesegment 2 d connecting between the pivot shaft 3 b and the pivot shaft 2b. Accordingly, when the parallel link (the main arm 5 and the sub-arm4) swings, the mold 1 is oscillated (swings) in the vertical directionabout the swing arm center 1 a along an arc with a certain curvatureradius.

A motor 10 is mounted on an installation floor with the pivot shaftbeing horizontally positioned. The rotary shaft of the motor 10 isprovided with an eccentric cam 9. The eccentric cam 9 and a pivot shaft7 at the other end of the main arm 5 are connected via a link 8.Accordingly, rotation of the motor 10 causes rotation of the eccentriccam 9, which in turn causes vertical movement of the link 8 via theeccentric cam 9. The vertical movement of the link 8 causes the main arm5 to swing, which in turn causes the sub-arm 4 to swing. In this way,the mold 1 is oscillated in the vertical direction.

FIG. 9 is a schematic diagram showing a hydraulic servo-type moldoscillator. In this hydraulic servo-type mold oscillator, a hydraulicservo cylinder 11 is installed in place of the eccentric cam. In thehydraulic servo cylinder 11, an upper end of a piston 12 is rotatablyconnected to a pivot shaft 7, so that the other end portion (pivot shaft7) of a main arm 5 is caused to reciprocate in the vertical direction bythe piston 12 driven by the hydraulic servo cylinder 11.

FIG. 10 is a schematic diagram showing an electrically driven servo-typemold oscillator. In this electrically driven servo-type mold oscillator,an electrically driven servo actuator 20 is installed in place of theeccentric cam shown in FIG. 8. FIG. 11 is a schematic diagram showingthe electrically driven servo actuator 20. A base 21 is mounted on aninstallation floor. A servo motor 22 and a cylinder tubes 33 areinstalled on the base 21. The servo motor 22 is installed so that arotary shaft 23 is positioned in the base 21 with the axial direction ofthe rotary shaft 23 being directed downward in the vertical direction.The rotary shaft 23 is provided with a pulley 24. A threaded shaft 29 ofa ball screw is rotatably installed via angular bearings 55 with theaxial direction of the threaded shaft 29 being directed in the verticaldirection, and a lower part of the threaded shaft 29 is positioned inthe base 21. A pulley 25 is fixed to a lower end portion of the threadedshaft 29. A belt 26 is looped between the pulley 24 and the pulley 25.Accordingly, forward and reverse rotation of the motor 22 causes forwardand reverse rotation of the threaded shaft 29 via the belt 26.Accordingly, in this embodiment, the pulleys 24 and 25, and the belt 26function as the power transmitting mechanism.

In the cylinder tube 33, a nut-side shaft 31 is fixed to a ball nut 30coaxially with the threaded shaft 29 that is positioned with the centralaxis thereof being directed in the vertical direction. The ball nut 30is screw-fitted on the threaded shaft 29 with balls interposedtherebetween. Forward and reverse rotation of the threaded shaft 29causes the ball nut 30 to move in the vertical direction. The nut-sideshaft 31 is fixed to the upper end of the ball nut 30 with the axialdirection of the nut-side shaft 31 being directed in the verticaldirection. The nut-side shaft 31 is supported by ball splines 34 so asto be able to move in the vertical direction. The upper end of thenut-side shaft 31 protrudes upward from an upper portion of the cylindertube 33. The upper end of the nut-side shaft 31 is connected to thepivot shaft 7 at the other end of the main arm 5.

In the electrically driven servo-type mold oscillator, the belt 26transmits rotational driving force produced by forward and reverserotation of the rotary shaft 23 of the servo motor 22 to the threadedshaft 29 in the cylinder tube 33, which causes forward and reverserotation of the threaded shaft 29. The forward and reverse rotation ofthe threaded shaft 29 causes the ball nut 30 screw-fitted on thethreaded shaft 29 to move in the vertical direction, which in turncauses the nut-side shaft 31 fixed to the upper end of the ball nut 30to move in the vertical direction. In this way, a main arm 5, to whichan upper end portion of the nut-side shaft 31 is connected via a pivotshaft 7, swings about a pivot shaft 3 b. The swinging motion of the mainarm 5 is followed by swinging motion of a sub-arm 4, which in turncauses a mold 1 to oscillate in the vertical direction.

PRIOR ART DOCUMENT Patent Document

[Patent Document 1] Japanese Translation of PCT internationalApplication Publication No. H11-506382 (JP 11-506982 A)

SUMMARY OF INVENTION Problems to be Solved by the Invention

However, in the eccentric cam-type mold oscillator, amplitude ofoscillation cannot be changed during casting operation. Moreover, apattern with time, or waveform, of oscillation of the mold is limited toa sinusoidal wave. In contrast, in the hydraulic servo-type moldoscillator, amplitude of oscillation of the mold can be changed evenduring casting operation by adjusting timing of control of the pressurefor advancing the piston 12 of the hydraulic servo cylinder 11 and thepressure for retracting the piston 12. Moreover, the pattern of the moldoscillation is not limited to a sinusoidal wave and it is possible toset a non-sinusoidal waveform. Also in the electrically drivenservo-type mold oscillator, amplitude of oscillation of the mold can bechanged even during casting operation. Moreover, the pattern of the moldoscillation can be set to either of a sinusoidal waveform and anon-sinusoidal waveform.

However, the hydraulic servo-type mold oscillator requires inspection offilters, hydraulic oil, etc. of the hydraulic servo cylinder 11.Moreover, it is required, to control contamination of the hydraulic oil.

In the case of the electrically driven servo-type mold oscillator, thenut-side shaft 31 is caused to move in the vertical direction by forwardand reverse rotation of the servo motor. In this case, the amplituderequired for the purpose of mold oscillation is small, that is, about ±6mm for example. This means that the amplitude of the vertical movementof the pivot shaft 7 of the main arm 5 is correspondingly small. Forthis reason, the rotation angle of the threaded shaft 29 tor swingingoperation is small and moreover, long-time continuous operation isrequired, which means that the threaded shaft 29 and the ball nut 30 arerequired to operate under severe conditions. Conventionally, ordinarygrease is used to lubricate the threaded shaft 29 and the ball nut 30.However, the threaded shaft 20 is repeatedly rotated forward andbackward within a small oscillatory rotation angle and therefore, thereis a possibility that breakdown of oil film occurs in the case of greaselubrication.

The present invention has been made in consideration of such a problemand an object of the present invention is to provide aneasy-to-maintain, electrically driven servo-type mold oscillator, withwhich it is possible to increase service life.

Means for Solving the Problem

A mold oscillator according to the present invention is a moldoscillator for oscillating a mold of a continuous casting machine,characterized by including:

a servo motor;

a ball screw unit that has a ball screw having a threaded shaft and aball nut, and a nut-side shaft fixed to the ball nut coaxially with thethreaded shaft, wherein the ball screw unit is positioned so that acentral axis of the ball screw unit extends in a vertical direction;

a power transmitting mechanism that transmits rotation of a rotary shaftof the servo motor to a first shaft that is one of the threaded shaftand the nut-side shaft of the ball screw unit that is positioned on alower side;

a casing that surrounds at least part of the ball screw, the casingbeing configured so as to be able to submerge the ball nut of the ballscrew and part of the threaded shaft of the ball screw, on which partthe ball nut is engaged with the threaded shaft, in a lubricating oil tolubricate the ball screw with an oil bath;

a lubricating oil tank that stores the lubricating oil;

a collection pipe for introducing the lubricating oil to the lubricatingoil tank, the collection pipe being connected to an outlet port providedin a lower portion of the casing; and

a supply device for resupplying the lubricating oil in the lubricatingoil tank into the casing through an inlet port provided above the outletport in the casing, wherein

a second shaft that is the other of the threaded shaft and the nut-sideshaft of the ball screw unit is connected to the mold side.

This mold oscillator may further include: a bearing supporting the firstshaft so that the first shaft can rotate about a central axis thereof;and a bearing retainer, in which a channel for communicating the outletport with a space between an inner race and an outer race of the bearingis formed, the bearing retainer being fixed under the bearing at aposition corresponding to a midpoint portion of the first shaft in alongitudinal direction thereof, wherein a seal contacting the firstshaft is included in the bearing retainer so as to prevent thelubricating oil from leaking downward.

In the mold oscillator according to the present invention, aconfiguration may be adopted, in which

the mold oscillator further includes:

a rotary parasol portion provided on a side surface of the first shaftof the ball screw unit below the bearing retainer and having a parasolshape widening downward, the rotary parasol portion being configured torotate with the first shaft; and

a stationary parasol portion fixed under the rotary parasol portion andhaving a parasol shape widening downward, the stationary parasol portionbeing disposed so as to at least partially overlap the rotary parasolportion in a radial direction, wherein

a drain outlet for discharging, into the outside, the lubricating oilreceived on the stationary parasol portion is provided in the casing.

In the mold oscillator according to the present invention, aconfiguration may be adopted, in which

a sealing member for sealing a gap between the casing and the secondshaft is detachably fitted.

The mold oscillator according to the present invention may furtherinclude an arm mechanism, having an arm extending in a lateraldirection, for oscillating the mold by moving the mold in the verticaldirection through swinging movement of the arm, wherein a fulcrum isprovided at a midpoint portion of the arm, one end of the arm isconnected to the second shaft, and the other end of the arm is connectedto the mold.

Effects of the Invention

According to the present invention, submerged in a lubricating oil inthe casing are a driving shaft that rotates forward and backward, abearing that rotatably supports the driving shaft, a ball screw that iscontinuous with the driving shaft, a ball nut that is screw-fitted onthe ball screw and converts forward and reverse rotation into verticalreciprocation, a driving bar that is connected to the ball nut and movesin the vertical direction, and ball splines that prevent the ball nutfrom rotating to allow the ball nut to move in the vertical directionand are engaged with the driving bar so as to allow the driving bar tomove in the vertical direction, and therefore, it is possible tosufficiently lubricate moving parts in the casing. Accordingly, it ispossible to significantly elongate life of the moving parts included inthe actuator of the mold oscillator.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing an electrically driven actuator120 of a mold oscillator according to an embodiment of the presentinvention.

FIG. 2 is a front sectional view showing the electrically drivenactuator 120 of the embodiment.

FIG. 3 is a partially enlarged view of the same.

FIG. 4 is a partially enlarged view of the same.

FIG. 5 is a side sectional view of the same.

FIG. 6 is a front sectional view of a bearing retainer 80.

FIG. 7 is a bottom view of the bearing retainer 80.

FIG. 8 is a diagram showing a conventional eccentric cam-type moldoscillator.

FIG. 9 is a diagram showing a conventional hydraulic servo-type moldoscillator.

FIG. 10 is a diagram showing a conventional electrically drivenservo-type mold oscillator.

FIG. 11 is a diagram showing an electrically driven actuator of theconventional electrically driven servo-type mold oscillator.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be specifically describedbelow with reference to the accompanying drawings. FIG. 1 is a schematicdiagram showing a concept of an electrically driven actuator 120 of amold oscillator according to the embodiment of the present invention.The electrically driven actuator 120 of the mold oscillator shown inFIG. 1 is obtained by further installing a lubricating oil tank 41 undera base 21 and a pump 40 for circulating a lubricating oil stored in thelubricating oil tank 41 through a cylinder tube 33, which functions asthe casing of the present invention, in addition to the electricallydriven actuator 20 shown in FIG. 11. The lubricating oil sent underpressure from the pump 40 is passed through a filter (not shown),supplied to an upper portion of the cylinder tube 33 via a supply pipe43, and collected from a lower portion of the cylinder tube 33 into thetank 41 through a collection pipe 42, whereby the lubricating oil iscirculated for lubrication of a threaded shaft 29 and a ball nut 30. Inthis embodiment, the threaded shaft 29 and the ball nut 30 are submergedin the lubricating oil bath, so that the threaded shaft 29 and the ballnut 30, which are oscillated within a small oscillatory rotation angleand operated for a long time, are lubricated without breakdown of oilfilm. Moreover, the lubricating oil is collected in the tank 41, so thatit is possible to easily determine the degree of degradation of thelubricating oil, which makes it possible to determine the timing ofperforming an overhaul of the actuator 120 of the mold oscillator. Notethat, in this embodiment, the supply device includes the supply pipe 43,the pump 40, and the filter (not shown).

Next, a structure of the electrically driven actuator 120 of thisembodiment will be described in detail. FIG. 2 is a front sectional viewshowing the electrically driven actuator 120, and FIGS. 3 and 4 arepartially enlarged views thereof. FIG. 5 is a side sectional view of thesame. The base 21 is mounted on an installation floor. The circularcylinder tube 33, the central axis of which is directed in the verticaldirection, is fixed in a standing position on the base 21, a bearingsupport portion 28 is provided under the cylinder tube 33, and angularbearings 55 are fitted into the bearing support portion 28. The threadedshaft 29 is rotatably supported by the angular bearings 55 with thecentral axis of the threaded shaft 29 being directed in the verticaldirection. In each of the bearings 55, an outer race 51 and an innerrace 52 are fixed, the outer race 51 supporting balls 50 on the outerside, the inner race 52 supporting the balls 50 on the inner side andbeing in contact with an outer circumferential surface of the threadedshaft 29. The balls 50 are held between the inner race 52 and the outerrace 51 so as not to fall out. In this way, the balls 50 rotate in astate where the balls 50 are held between the inner race 52 and theouter race 51, so that the threaded shaft 29 is supported so as to berotatable about the central axis thereof. In the present invention, itsuffices to position the ball screw so that the central axis thereofextends, or stretches, in the vertical direction, that is, the ballscrew may be disposed in an inclined position. However, when the ballscrew is positioned so that the central axis thereof is directed in thevertical direction as in the case of this embodiment, it is possible tosecure high stability and durability.

The ball nut 30 is disposed in this cylinder tube 33 and is screw-fittedon the threaded shaft 29 with the balls interposed therebetween. In thecylinder tube 33, a nut-side shaft 31 fixed to the ball nut 30 coaxiallywith the threaded shaft 29 is also disposed. Specifically, a lower endportion of the nut-side shaft 31 is fixed to an upper end portion of theball nut 30. Accordingly, in this embodiment, the threaded shaft 29functions as the first shaft of the present invention and the nut-sideshaft 31 functions as the second shaft. Ball splines 34 are fixed to aninner surface of the cylinder tube 33 at a position corresponding to thenut-side shaft 31. The nut-side shaft 31 is supported by the ballsplines 34 so as to be able to reciprocate in the vertical direction andso as not to be rotatable. Since the nut-side shaft 31 is supported bythe ball splines 34 so as not to be rotatable, the nut-side shaft 31cannot rotate about the central axis thereof. Accordingly, forward andreverse rotation (oscillatory rotation) of the threaded shaft 29 aboutthe central axis thereof causes the ball nut 30, which is screw-fittedon the threaded shaft 29 with the balls interposed therebetween, toreciprocate in the vertical direction within a range corresponding tothe oscillatory rotation angle. The nut-side shaft 31 is supported bythe ball splines 34 so as to be able to move in the vertical directionand so as not to be rotatable and therefore, the nut-side shaft 31 fixedto the ball nut 30 moves in the vertical direction within the rangeequal to that of the ball nut 30. A cylindrical stopper 63 is disposedso as to surround she threaded shaft 29. A sealing member 65 for sealinga gap is detachably fitted between the cylinder tube 33 and the nut-sideshaft 31. The nut-side shaft 31 continuously oscillates in the verticaldirection and therefore, the sealing member of this portion wearsseverely. When the sealing member 65 is detachably fitted in this way,it it possible to avoid a situation where the entire cylinder tube 33must be replaced because of wear of the portion contacting the nut-sideshaft 31 (second shaft).

An upper end of the nut-side shaft 31 protrudes upward from the upperportion of the cylinder tube 33. Of the mold oscillator side and themold side, the upper end of the nut-side shaft 31 is connected to themold side. In this embodiment, the upper end of the nut-side shaft 31 isprovided with a connection portion 61, which is rotatably connected to apivot shaft 7 of a main arm 5. When the nut-side shaft 31 moves in thevertical direction, the main arm 5 swings and oscillates the mold. Whena configuration is adopted, in which the mold oscillator is directlyconnected to a trunnion of the mold, for example, the upper end of thenut-side shaft is directly connected to the trunnion of the mold. Incontrast, when a configuration is adopted, in which the mold oscillatoris connected to the mold side via the main arm 5 as described above, itis possible to install the mold and the mold oscillator at separatesections with a partition wall 6 interposed therebetween, so that it ispossible to avoid installing the mold oscillator in a high-temperatureenvironment around the mold.

A motor is installed on the base 21 in parallel with the cylinder tube33. A rotary shaft 23 of the motor 22 is inserted into the base 21 withthe rotation axis of the rotary shaft 23 being directed in the verticaldirection. The rotary shaft 23 is provided with a pulley 24. The part ofthe threaded shaft 29 that is inserted in the base 21 is provided with apulley 25. A belt 26 is looped between the pulleys 24 and 25, so thatoscillatory rotation of the rotary shaft 23 of the motor 22 istransmitted to the threaded shaft 29 via the belt 26.

The lubricating oil tank 41 provided below the base 21 and thelubricating oil in the lubricating oil tank 41 is supplied to an inletport 90 (see FIG. 5) provided in the upper portion of the cylinder tube33 via the supply pipe 43 (see FIG. 1) by the small pump 40 providedabove the lubricating oil tank 41. The lubricating oil supplied into thecylinder tube 33 is collected into the lubricating oil tank 41 from anoutlet port 91 provided in the lower portion of the cylinder tube 33through the collection pipe 42 (see FIGS. 1 and 2). The position, atwhich the inlet port is provided, is not particularly limited as long asthe inlet port is provided above the outlet port. However, it ispreferable that the inlet port be provided above an element forsupporting the second shaft (the nut-side shaft 31 in this embodiment)so as to be movable in the vertical direction and so as not to berotatable, such as ball splines, as in the case of this embodiment. Byso doing, the lubricating oil for lubricating the supporting element isalso supplied by the supply device through the filter, so that it ispossible to perform lubrication with the use of the lubricating oil,from which contaminants have been removed.

A bearing retainer 80 is fixed at the bottom surface of the angularbearings 55. FIG. 6 is a front sectional view of the bearing retainer80. FIG. 7 is a bottom view of the bearing retainer 80. The bearingretainer 80 has a circular ring shape and has a three stepped structure,including an inner hole 84 at the upper surface that has the smallestradius, a middle hole 82 that is formed below the inner hole 84, and alower hole 83 that is formed below the middle hole 82. At the uppersurface of the bearing retainer 80, an upper end 85 that has a radiussmaller than that of the outermost edge or the bearing retainer 80 isformed as a step. Part of the upper surface of the bearing retainer 80is slightly lowered to form a hollow 81 in the radially inner side ofthe upper end 85. the upper end 85 has a diameter the same as that ofthe outer edge of the bearings 55. The retainer 80 is fixed to thebottom surface of the bearing support portion 28 by screws with theupper end 85 being in contact with the bearing 55. A seal 74 is fittedinto the middle hole 82 of the retainer 80. A metal ring 73 is disposedso as to be fitted onto the threaded shaft 29 between the seal 74 andthe threaded shaft 29. Under the metal ring 73, a cylindrical fixingmember 76 is fixed so as to be fitted onto the threaded shaft 29, and aparasol shaped member, which has a cone shape widening downward and hasa horizontal ring shaped portion at the upper end, is sandwiched betweenthe metal ring 73 and the fixing member 76, forming a rotary parasolportion 71. The seal 74 is fixed to the retainer 80 so as not to beseparated from the retainer 80 by fixing a circular ring shapedretaining plate 75 to the bottom surface of the retainer 80 by screws.

An oval counterbored hole portion 85 a is formed on the upper surfaceside of the retainer 80 in a portion extending from the hollow 81 to theradially outer side of the upper end 85, and a channel 87 passingthrough the retainer 80 in a plate thickness direction is formed in abottom portion of the counterbored hole portion 85 a in a radially outerside. The lubricating oil flows out of the outlet port 90 through thechannel 87 in the retainer 80 and is introduced into the lubricating oiltank 41 via the collection pipe 42.

The rotary parasol portion 71 is formed by fitting the parasol shapedmember, which has the cone shape widening downward and has thehorizontal ring shaped portion at the upper end, onto the threaded shaft29 and sandwiching the horizontal ring shaped portion between the metalring 73 and the fixing member 76 to fix the parasol shaped member to thethreaded shaft 29. A stationary parasol portion 72 is formed by fixing ahorizontal portion 72 a of a parasol shaped member to an upper surfaceof the base 21, which parasol shaped member has a cone shaped portion 72b widening downward at an angle the same as that of the cone shapedportion of the rotary parasol portion 71 and has the horizontal portion72 a extending horizontally outward from the lower end of the coneshaped portion 72 b. An opening 70, through which the threaded shaft 29is passed, is formed in a top wall of the base 21. The horizontal,portion 72 a of the parasol shaped member forming the stationary parasolportion 72 is fixed to a peripheral portion around the opening 70. Therotary parasol portion 71 that rotates with the threaded shaft 29 andthe stationary parasol portion 72 that is fixed to the base 21 aredisposed so that the rotary parasol portion 71 is positioned on theupper side of the stationary parasol portion 72 and the cone shapedportions of these parasol portions at least partially overlap each otherin the radial direction around the entire circumference. A drain outlet93 for discharging, into the outside, the lubricating oil received onthe upper surface of the stationary parasol portion 72 is provided inthe bearing support portion 28. By so doing, even when the lubricatingoil leaks from the inner edge of the retainer 80 onto the rotary parasolportion 71 because of, for example, deterioration of the seal 74, thelubricating oil flows on the cone shaped portion of the rotary parasolportion 71 and the cone shaped portion of the stationary parasol portion72 to be introduced onto the horizontal portion 72 a of the stationaryparasol portion 72, and is then discharged into the outside from thedrain outlet 93. Accordingly, even when the lubricating oil leaksdownward from the inner edge of the retainer 80, the lubricating oil isprevented from leaking to the area under the stationary parasol portion72 to reach the pulley 25 or the belt 26. In this embodiment, thelubricating oil discharged from the drain outlet 93 into the outside isnot collected into the lubricating oil tank, that is, discarded into theoutside.

As described above, in this embodiment, operation is performed in astate where the threaded shaft 29 and the ball nut 30 are submerged inthe lubricating oil, so that wear is significantly reduced. This makesit possible to increase life of the actuator of the mold oscillator.Moreover, providing the rotary parasol portion 71 and the stationaryparasol portion 72 makes it possible to obtain more secure sealingagainst leakage of the lubricating oil to prevent the lubricating oilfrom entering the inside of the base 21, so that it is possible toprevent the lubricating oil from adhering to the pulleys 24 and 25 andthe belt 26 in the base 21 to hamper operation thereof and to preventdeterioration of the belt.

While the present invention has been described with reference to theembodiments, the present invention is not limited to the above-describedembodiments. The scope of the present invention is determined based onthe attached claims and all the configurations obtained by omitting,changing, and/or improving the constituent elements within the scope ofthe present invention are also included in the present invention.

For example, while a configuration is described in the aboveembodiments, in which the first shaft, one of the threaded shaft and thenut-side shaft included in the ball screw unit of the present inventionthat is positioned on the lower side, is the threaded shaft, thenut-side shaft may be positioned on the lower side as the first shaft.That is, the ball screw unit may be disposed in an inverted positionrelative to the position in the case of the above embodiments.

While the outlet port of the present invention is provided below thebearings in the lower portion of the casing in the above embodiments,the outlet port may be provided above the bearings in the lower portionof the casing as long as the upper or lower end of the bearings isliquid-tightly sealed. However, when a configuration is adopted, inwhich the outlet port is provided below the bearings and the lubricatingoil is passed through the space between the inner races and the outerraces of the bearings and is then collected as in the case of the aboveembodiments, it is possible to prevent contaminants from remaining inthe bearings.

DESCRIPTION OF REFERENCE NUMERALS

5: main arm

7: pivot shaft

21: base

22: motor

23: rotary shaft

24,25; pulley

26: belt

28: bearing support portion

29: threaded shaft

30: ball nut

31: nut-side shaft

32: ball screw

33: cylinder tube

34: ball spline

40: pump

41: lubricating oil tank

42: collection pipe

43: supply pipe

50: ball

51: outer race

52: inner race

55: angular bearing

87: channel

90: inlet port

91: outlet port

93: drain outlet

120: electrically driven actuator

1. A mold oscillator for oscillating a mold of a continuous castingmachine, comprising: a servo motor; a ball screw unit that includes aball screw having a threaded shaft and a ball nut, and a nut-side shaftfixed to the ball nut coaxially with the threaded shaft, wherein theball screw unit is positioned so that a central axis of the ball screwunit extends in a vertical direction; a power transmitting mechanismthat transmits rotation of a rotary shaft of the servo motor to a firstshaft that is one of the threaded shaft and the nut-side shaft of theball screw unit that is positioned on a lower side; a casing thatsurrounds at least part of the ball screw, the casing being configuredso as to be able to submerge the ball nut of the ball screw and part ofthe threaded shaft of the ball screw, on which part the ball nut isengaged with the threaded shaft, in a lubricating oil to lubricate theball screw with an oil bath; a lubricating oil tank that stores thelubricating oil; a collection pipe for introducing the lubricating oilto the lubricating oil tank, the collection pipe being connected to anoutlet port provided in a lower portion of the casing; and a supplydevice for resupplying the lubricating oil in the lubricating oil tankinto the casing through an inlet port provided above the outlet port inthe casing, wherein a second shaft that is the other of the threadedshaft and the nut-side shaft of the ball screw unit is connected to themold side.
 2. The mold oscillator according to claim 1, furthercomprising: a bearing supporting the first shaft so that the first shaftcan rotate about a central axis thereof; and a bearing retainer, inwhich a channel for communicating the outlet port with a space betweenan inner race and an outer race of the bearing is formed, the bearingretainer being fixed under the bearing at a position corresponding to amidpoint portion of the first shaft in a longitudinal direction thereof,wherein a seal contacting the first shaft is included in the bearingretainer so as to prevent the lubricating oil from leaking downward. 3.The mold oscillator according to claim 2, further comprising: a rotaryparasol portion provided on a side surface of the first shaft of theball screw unit below the bearing retainer and having a parasol shapewidening downward, the rotary parasol portion being configured to rotatewith the first shaft; and a stationary parasol portion fixed under therotary parasol portion and having a parasol shape widening downward, thestationary parasol portion being disposed so as to at least partiallyoverlap the rotary parasol portion in a radial direction and astationary parasol portion fixed under the rotary parasol portion andhaving a parasol shape widening downward at an angle the same as that ofthe rotary parasol portion, the stationary parasol portion beingdisposed so as to partially overlap the rotary parasol portion in aradial direction around an entire circumference, wherein a drain outletfor discharging, into the outside, the lubricating oil received on thestationary parasol portion is provided in the casing.
 4. The moldoscillator according to claim 1, further comprising a sealing member forsealing a gap between the casing and the second shaft, the sealingmember being detachably fitted.
 5. The mold oscillator according toclaim 1, further comprising an arm mechanism, including an arm extendingin a lateral direction, for oscillating the mold by moving the mold inthe vertical direction through swinging movement of the arm, wherein afulcrum is provided at a midpoint portion of the arm, one end of the armis connected to the second shaft, and the other end of the arm isconnected to the mold.